Peroxycarboxylic acid compositions have been reported to be effective antimicrobial agents. Methods to clean, disinfect, and/or sanitize hard surfaces, meat products, living plant tissues, and medical devices against undesirable microbial growth have been described (e.g., U.S. Pat. No. 6,545,047; U.S. Pat. No. 6,183,807; U.S. Pat. No. 6,518,307; U.S. Pat. No. 5,683,724; and U.S. Patent Application Publication No. 2003/0026846). Peroxycarboxylic acids have also been reported to be useful in preparing bleaching compositions for laundry detergent applications (U.S. Pat. No. 3,974,082; U.S. Pat. No. 5,296,161; and U.S. Pat. No. 5,364,554).
Peroxycarboxylic acids can be prepared by the chemical reaction of a carboxylic acid and hydrogen peroxide (see Organic Peroxides, Daniel Swern, ed., Vol. 1, pp 313-516; Wiley Interscience, New York, 1971). The reaction is usually catalyzed by a strong inorganic acid, such as concentrated sulfuric acid. The reaction of hydrogen peroxide with a carboxylic acid is an equilibrium reaction, and the production of peroxycarboxylic acid is favored by the use of an excess concentration of peroxide and/or carboxylic acid, or by the removal of water.
Some peroxycarboxylic acid-based disinfectants or bleaching agents are comprised of an equilibrium mixture of peroxycarboxylic acid, hydrogen peroxide, and the corresponding carboxylic acid. One disadvantage of these commercial peroxycarboxylic acid cleaning systems is that the peroxycarboxylic acid is oftentimes unstable in solution over time. One way to overcome the stability problem is to generate the peroxycarboxylic acid prior to use by combining multiple reaction components that are individually stable for extended periods of time. Preferably, the individual reaction components are easy to store, relatively safe to handle, and capable of quickly producing an efficacious concentration of peroxycarboxylic acid upon mixing.
The CE-7 family of carbohydrate esterases has recently been reported to have perhydrolase activity. These “perhydrolase” enzymes have been demonstrated to be particularly effective for producing peroxycarboxylic acids from a variety of carboxylic acid ester substrates when combined with a source of peroxygen (See WO2007/070609 and U.S. Patent Application Publication Nos. 2008/0176299, 2008/176783, and 2009/0005590 to DiCosimo et al.; each herein incorporated by reference in their entireties). Some members of the CE-7 family of carbohydrate esterases have been demonstrated to have perhydrolytic activity sufficient to produce 4000-5000 ppm peracetic acid from acetyl esters of alcohols, diols, and glycerols in 1 minute and up to 9000 ppm between 5 minutes and 30 minutes once the reaction components were mixed (DiCosimo et al., U.S. Patent Application Publication No. 2009/0005590).
The ability to commercialize many bleaching and/or disinfection products based on enzymatic perhydrolysis may be dependent upon the cost of producing the enzyme catalyst. The use of enzyme catalysts having improved perhydrolytic activity may reduce the amount of enzyme catalyst in the commercial product and may significantly decrease the cost of production. As such, there remains a need to identify enzyme catalysts having improved perhydrolytic activity.
Further, enzymatic perhydrolysis is typically conducted using aqueous reaction conditions. Enzyme catalysts having perhydrolytic activity typically exhibit hydrolytic activity, forming carboxylic acids that may lower the pH of the reaction mixture. As such, it is desirable to utilize a perhydrolase that has high selectivity for perhydrolysis of an ester to peroxycarboxylic acid relative to hydrolysis of the same ester to carboxylic acid; the “P/H” ratio (rate of perhydrolysis/rate of hydrolysis) is one method of characterizing the selectivity of a perhydrolase for perhydrolysis.
The problem to be solved is to provide enzyme catalysts characterized by improved perhydrolytic activity. The improvement may be an increase in perhydrolase specific activity for carboxylic acid esters and/or an improvement in selectivity for perhydrolysis over hydrolysis when producing peroxycarboxylic acids from carboxylic acid esters.